Aluminium

Aluminium

The element aluminium has been a topic of discussion among reefkeepers, especially since the introduction of ICP analyses. The main reason for this is probably the frequent detection of this element in aquarium water. Aluminium is one of the most common elements in the earth’s crust and is naturally found in small quantities in seawater.

Biological functions of aluminium in coral or bacterial physiology are largely unknown. We do not currently assume any function that is important for us and therefore adjust the dosage to the natural concentration value.

However, aluminium in reef aquaria may differ from that in natural seawater. Due to its special water chemistry, saltwater can dissolve more aluminium ions than freshwater, and due to the high organic load in aquaria, the aluminium content may well rise to 1,000 ppm/l(0,26 US.liq.gal.). However, more than 200 ppm/l(0,26 US.liq.gal.) should not be reached, otherwise long-term damage can be expected.

Aluminium also occurs in seawater as colloidal or particulate matter. Particularly in closed aquarium systems, we have to deal with aluminium particles much more often than with dissolved aluminium. The reason is the use of minerals containing aluminium in feed, sea salts, the technology used, or in water treatment.

During the recent years, we have carried out several investigations on this topic. In addition to selected customer aquaria, we also examined facilities from our coral propagating facility, e.g. with the aid of our ICP/OES analysis, and this way we collected data on the type of aluminium contamination in reef tanks and the change in concentration. Hundreds of individual measurements were necessary to obtain a significant data pool. Due to the special method we use to measure aluminium in seawater, we are able to accurately determine even very low concentrations.

If, on the other hand, artemia brine shrimp is fed, aluminium is partly present in dissolved form. We were able to detect up to 1,000 mg/kg(2,2 lbs.) of aluminium in Artemia freeze-dried food plates. Feedstuffs that use artemia as a base can also be contaminated with aluminium. Go without such products, especially since artemia is not an ideal food for marine animals when seen as a whole. They have little nutritional value and, in addition to aluminium, they also supply water with other trace elements and pollutants, sometimes in such large quantities that harmful effects occur.

Products that are used to stabilise the calcium balance may also contain some aluminium. This also applies to various calcium reactor filling substrates. Depending on the batch and source, such impurities are often at different levels. However, the total amounts of inputs from this source are usually too small to be significant.

However, the filtering of the water via zeolite systems, aluminium-containing PO4 adsorbers and organic adsorbers always have an influence on the aluminium values of the water. Zeolites consist of minerals of the aluminium silicate group. As these minerals are quite soft and are removed in the filters, higher aluminium values are obtained. Especially in zeolite filters which are cleaned daily, there are micro-particle discharges, which increase the aluminium measurement value. However, since here almost only particulate material is present, it is negligible in this case.

We also tested some salt mixtures over a longer period of time. The good news is that aluminium is practically undetectable in almost all brand salts. Only in two of these sea salt mixtures, a few micrograms of aluminium could be detected, but still within the range of natural values.

In addition to sea salt mixtures, also animal feed can be considered as a source of higher aluminium values. Here, it depends both on the type of production and the raw materials used. The origin and quality of the raw materials and binding agents are relevant for the input of aluminium. With good feed granulates, benthonites (aluminium silicates) are used to bind the feed particles. Although this results in higher aluminium values in analyses, it is completely harmless, since in such a case it is a particulate material.

With PO4 adsorbers based on aluminium, however, the situation is somewhat different. At high pH-values, aluminium dissolves better from materials than it does at low pH-values. Unactivated alumina therefore releases relatively large amounts of aluminium. Activated adsorbers (round white spheres) release considerably less. Also pay attention to a low flow rate of approx. 200 l/h(50-55 US.liq.gal./h) in order to use the adsorbers optimally. Under no circumstances should aluminum-based PO4 adsorbers be able to whirl in the filter and rub off each other.

It is not yet clear how much aluminium can enter the water from the released particles. Therefore, regular monitoring of the animals is advisable, as well as the water itself. If the measured values are too high, a reduction of the input source can quickly reduce it, as can filtering via iron adsorbers.

Leather corals (e.g. Sarcophyton or Sinularia), stoloniferans (e.g. Clavularia or Knopia) are good indicator species. If your aquarium water has elevated aluminium values, you should observe these coral species genera well. If the polyp expansion is incomplete and the animals change quickly between expanded and contracted state, the probability of increased aluminium levels in the water is quite high. From approx. 300 µg/l(0,26 US.liq.gal.) aluminium, leather corals, stoloniferans, zoanthids and other species hardly open their polyps or even remain closed all the time. It should also be noted that the higher their metabolism, the faster the animals will show a reaction. Partial water change and filtration via Iron adsorbers will be very helpful here. Of course, the aluminium source must be located and removed.